Provided is an energy source device that is used with a treatment tool comprising a bipolar electrode and a heater. The energy source device includes a processor that: executes output control, in relation to output to the heater, for causing the heater to reach a target temperature and maintaining the heater at the target temperature; and in the output control based on the target temperature, detects a parameter associated with the heater temperature and/or output to the heater. On the basis of the detected parameter, the processor sets a threshold to be used for determining whether to stop or reduce output to the bipolar electrode.